The overall goal of this project is to develop therapeutic antivirals to treat life-threatening flavivirus infections. Enfuvirtide, a clinically successful peptide HIV fusion inhibitor, is the prototype for a new class of antivirals that inhibit viral envelope protein structural rearrangements essential for viral entry into host cells. In preliminary experiments, we screened a phage display library for proteins and peptides that bind recombinant West Nile (WN) virus envelope protein. WN virus peptides with affinity for envelope protein were also rationally selected from the envelope protein structure. These studies identified 6 proprietary peptides that bind recombinant WN virus envelope protein and inhibit WN virus infection of cultured cells. In this project, we will identify additional peptides that block WN and dengue virus infections. Selected peptides will be modified to produce broad-spectrum peptides that target multiple flaviviruses. The project will also initiate high throughput screening of chemical compound libraries for antiviral small molecules that compete with the neutralizing peptides for binding to envelope protein. Candidate antiviral compounds will be evaluated for neutralization of flaviviruses, including the 4 serotypes of dengue virus, and for ability to protect mice against dengue and WN virus infections. This experimental approach will be expanded in Phase II to develop a panel of modified peptides and small molecules that are candidates for development as human therapeutics. This project will provide clinicians and public health officials with new means to manage natural, accidental and intentional flavivirus outbreaks. [unreadable] [unreadable] [unreadable]